Help With Multiplication and Percents

Date: 11/11/96 at 19:24:42
From: Amanda Oakley
Subject: Math
Dear Dr. Math,
I am in grade five and have lots of trouble! My class is a mix of
fifth and sixth graders so we are doing percentages, which are really
hard for me because I am not very good at multiplication and anything
else in that area. Can you please help me?
Sincerely,
Amanda Oakley

Date: 11/23/96 at 15:44:27
From: Doctor Lim
Subject: Re: Math
Dear Amanda,
Don't worry so much. If you put time and effort towards your study
of mathematics, soon you will see results. You are already taking a
good first step by figuring out what areas are hard for you, like
multiplication. If this is the root of your troubles, I can try to
help you fix it.
There is no easy way to learn multiplication. If you understand the
concept of multiplication, the only way to improve your skills is to
practice what you have learned.
Most of the time problems seem difficult only because they look big
and scary. Problems became less frightening when you break them up
and see them as little pieces. You do not eat a whole cake up in one
mouthful, do you? You have to bite it into pieces or cut it up into
slices before eating it, right?
So if you learn your multiplication tables, everything else will fall
into place. My students find learning nine times tables to be the
hardest. After using this method it becomes easier for them:
Put your hands flat, palms down, on the table. Number your fingers
like this:
Left Hand Right Hand
1 2 3 4 5 6 7 8 9 0
If you have difficulty remembering this, try writing the numbers on
the backs of your hands.
Think of a number to multiply by 9.
Let's try 7 x 9:
Tuck your 7th finger underneath your palm.
You should have 6 fingers open to the left of your hidden finger and 3
fingers open to the right of it.
7 x 9 = 63
Now try it out with 4 x 9:
Tuck your 4th finger underneath your palm.
You should have 3 fingers open to the left of your hidden finger and 6
fingers open to the right of it.
4 x 9 = 36
Got it ?
For the rest of the multiplication tables, try looking at this site,
which teaches multiplication tables as a song:
http://www.schoolhouserock.com/multrock/
The key to finding percents is to recognize that a percent is just a
different way of writing a decimal.
Let us start with an example. Suppose we are given a group of 100
people, 70 of whom are men and 30 of whom are women.
This means that 70 out of 100 or 70/100 of the group are men.
There are lots of different ways to write 70 out of 100:
70/100
0.70
70 per cent
70%
70% of the people are men
Let us look at another example. Suppose that in my library there are
100 books, 40 of which are big and 60 of which are small. There are
lots of different ways to write 40 out of 100:
40/100
0.40
40 per cent
40%
40% of my library books are big books.
The notion of percent is very closely related to fractions, which you
can see by noticing that 40 out of 100 means:
40/100 = 4/10 = 2/5 = 0.40 = 40%
Math is just like a big family. All of its parts are related to each
other. If you can understand one part, the other parts are not that
difficult.
Please get back to me if you have problems.
-Doctor Lim, The Math Forum
Check out our web site! http://mathforum.org/dr.math